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[RFC,v3,07/15] x86/speculation/mds: Make mds_idle_clear forceful

Message ID 20241119153502.41361-8-vschneid@redhat.com (mailing list archive)
State RFC
Headers show
Series context_tracking,x86: Defer some IPIs until a user->kernel transition | expand

Checks

Context Check Description
netdev/tree_selection success Not a local patch

Commit Message

Valentin Schneider Nov. 19, 2024, 3:34 p.m. UTC 
Later commits will cause objtool to warn about non __ro_after_init static
keys being used in .noinstr sections in order to safely defer instruction
patching IPIs targeted at NOHZ_FULL CPUs.

mds_idle_clear is used in .noinstr code, and can be modified at
runtime (SMT hotplug). Suppressing the text_poke_sync() IPI has little
benefits for this key, as hotplug implies eventually going through
takedown_cpu() -> stop_machine_cpuslocked() which is going to cause
interference on all online CPUs anyway.

Mark it as forceful to let the kernel know to always send the
text_poke_sync() IPI for it, and to let objtool know not to warn about it.

Signed-off-by: Valentin Schneider <vschneid@redhat.com>
---
 arch/x86/kernel/cpu/bugs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 47a01d4028f60..dcc4d5d6e3b95 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -114,7 +114,7 @@  DEFINE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
 DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
 
 /* Control MDS CPU buffer clear before idling (halt, mwait) */
-DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
+DEFINE_STATIC_KEY_FALSE_FORCE(mds_idle_clear);
 EXPORT_SYMBOL_GPL(mds_idle_clear);
 
 /*